In situ Raman spectroscopic studies on the current oscillations during gold electrodissolution in HCl solution

Abstract

Raman spectroscopy has been used for investigating the gold oscillatory electrodissolution processes in a 2 mol dm −3 HCl solution. The vibration bands for Au–Cl −, AuCl 4 − and Au–O(H) as a function of potential, the spatial profile of AuCl 4 − concentration in the diffusion layer, and the temporal evolution of AuCl 4 − during the current oscillations have all been measured in situ by a confocal Raman spectroscope. These experimental results indicate that the transition between active and passive states of gold accounts for the current oscillations in a very narrow potential range. A crossing cycle in the cyclic voltammogram that means a pair of overlapping positive and negative feedbacks corresponds to the active–passive transition. A possible oscillatory electrodissolution mechanism has been proposed on the basis of the experimental results.